1. Field of the Invention
This invention relates to a process for the vapor phase oxidative dehydrogenation of monohydric alcohols to form the corresponding aldehydes and ketones. More particularly, this invention relates to the oxidative dehydrogenation of alcohols to aldehydes and ketones using a gold catalyst.
2. The Prior Art
Aldehydes and ketones markedly influence the odor of many essential oils and the very satisfactory effects that can be achieved with these odoriferous compounds have long been known to perfumers.
Aldehydes and ketones exhibiting desirable olfactive properties include both those found in natural products such as essential oils and fruits of plants and those which are made synthetically. Examples of odoriferous aldehydes include n-valeraldehyde (occurring in musk, herbs), isovaleradldehyde (occurring in peppermint, clove, citronella Oils) n-hexenal (occurring in eucalyptus oils), .alpha.,.beta.-hexenal or .beta.-propyl acrolein (occurring in green vegetables), n-heptaldehyde (not naturally occurring), n-octyl aldehyde (occurring in lemon oil, lemongrass oil), n-nonyl aldehyde (occurring in mandarin, orris root, Ceylon cinnamon), n-capraldehyde (occurring in sweet orange, lemongrass, mandarin neroli, coriander), n-undecylaldehyde (not naturally occurring), n-dodecylaldehyde (occurring in oils of silver fir, lemon and rue), n-tridecylic aldehyde (not naturally occurring), n-tetradecyl aldehyde (occurring in ocotea, pinus, and Formosan camphor oils), n-hexadecanal, n-octadecanal, phenyl octaldehyde (occurring in neroli oil), benzaldehyde (occurring in rose, peach, apricot) and p-tert-butyl-alpha methyl hydrocinnamaldehyde (Lilial, trademark). Examples of odoriferous ketones include ionone (occurring in flower oil, violet moss, and costus root), methyl ionone (not naturally occurring), dibenzyl ketone (not naturally occurring), methyl nonyl ketone (occurring in rue oil), zingerone (occurring in oil of ginger), dehydrojasmone (not naturally occurring), menthone (occurring in peppermint, pennyroyal and geranium) and ethylamyl ketone (occurring in lavender oil).
These odoriferous aldehydes and ketones are so potent that when they occur naturally, they are frequently present in natural oils in fractions on the order of 1%, but are so strongly odoriferous that they markedly affect the character of a perfume or formulation to which they are incorporated. When prepared synthetically, the purity of the aldehydes or ketones is a controlling factor in their commercial use, as the presence of unpleasant by-odors resulting from by-products formed during the synthesis can make their use in perfume formulations totally unacceptable.
The art is continually seeking methods of preparing odoriferous aldehydes and ketones synthetically wherein the reaction product has reduced concentrations of objectionable by-products.
One method of preparing aldehydes which has attained fairly large scale and widespread use is the oxidative dehydrogenation of monohydric alcohols which involves mixing an oxygen-containing gas (such as air) with the alcohol and passing this mixture over or through a suitable catalyst.
The catalytic oxidative dehydrogenation reaction may be represented by the following equation: ##STR1## where R represents branched and straight chain alkyl and alkenyl radicals having 1 to 16 carbon atoms, cycloalkyl and cycloalkenyl radicals having 5 to 16 carbon atoms, mononuclear and dinuclear aryl radicals and aralkyl radicals having 6 to 16 carbon atoms.
If the alcohol used in the catalytic oxidative dehydrogenation reaction is a secondary alcohol, the reaction product is a ketone in accordance with the following equation: ##STR2## where R' is selected from the same group of radicals as R and may be the same or a different radical than R.
Copper and silver alone or in combination with each other or with another metal such as zinc or chrome, metal oxides such as zinc oxide, iron oxide, molybdenum oxide and rare earth oxides are used by the art as catalysts for the oxidative dehydrogenation of alcohols.
These catalysts are subject to certain disabilities such as short life and undesirable by-products which render their replacement by a more suitable catalyst highly desirable.